Vehicles with internal combustion engines use catalytic converters to convert exhaust constituents and reduce regulated emissions. However, in some converters, conversion efficiency can be low at ambient temperatures. As such, various approaches have been used to increase exhaust heat during engine starting to thereby obtain earlier increased conversion efficiency.
One such approach is described in U.S. Pat. No. 6,725,830, which uses different ignition timing in different cylinder groups to increase total exhaust heat to the catalyst/exhaust, while still providing accurate idle speed control, among other features. In one example, the ignition timing of one group is significantly retarded after top dead center so that little torque is produced, but large quantities of heat are produced. Then, the remaining cylinders operate at higher load, which also increases exhaust heat, while retaining accurate torque control.
However, the inventors herein have recognized that such operation can be further improved by tailoring the valve operation of the different cylinder groups to the particular ignition timing conditions of those cylinders. As one example, the valve timing that provides improved combustion heat to the exhaust in the cylinders with significantly retarded ignition timing may be different than the valve timing that provides the most efficient and stable combustion in the cylinders with less ignition timing retard.
As such, a method for operating an engine having at least a first and second cylinder is provided. The first cylinder may have a first electrically actuated valve and the second cylinder may have a second electrically actuated valve. The method comprises operating the first cylinder with a spark timing more retarded than a spark timing of a second cylinder, where during said operation, said first cylinder operates with a first operation of said first electrically actuated valve and said second cylinder operates with a second operation of said second electrically actuated valve, where said first operation is different from said second operation.
As noted above, the different operations may include different valve timing. In this way, the combustion of each cylinder can be improved to further increase exhaust heat and more rapidly heat the exhaust, while still maintaining tight control of engine torque, or idle speed, for example. Note that various other types of differing valve operation may be used, such as lift, number of active/deactivated valves, and/or valve patterns.
In another aspect, a method for operating an engine having at least a first and second cylinder group is provided. The method comprises: operating the first cylinder with a spark timing substantially more retarded than a spark timing of a second cylinder, where during said operation, each cylinder of said first cylinder group operates with a first number of active valves and each cylinder of said second cylinder group operates with a second number of active valves, where said first number is different from said second number.
In this way, different cylinder charge motion and/or air amounts may be provided between the cylinders thereby providing appropriate conditions for each of the cylinders to enable each cylinder to provide improved operation.